1. Field of the Invention
The invention is in the field of motion estimation for frame stabilization using image-processing techniques. It is desired to have a technique with reduced complexity and that is suitable for hardware implementations. It is also desired to have a technique that can be used for fast global and local motion estimation, as well as image registration.
2. Description of the Related Art
Video sequences are known to be captured with hand-held digital still cameras often containing unwanted motion as a result of hand jitter. The motion caused by hand jitter can reduce the quality of the recorded video sequences. This movement is a biological phenomenon and the effect it has on the recorded video sequences is amplified by small and lightweight modern cameras. To reduce the influence of the hand-jitter motion, multiple image stabilization approaches have been proposed. When selecting one, a trade-off is to be made between different parameters of the system such as weight, performance, and cost.
One approach is optical image stabilization (OIS) which provides high performance. However, OIS is an expensive solution, and it has been used on high-end digital single lens reflex cameras, video cameras, and binoculars.
A second approach is electronic image stabilization (EIS) which involves use of extra hardware such us gyroscopic sensors. Gyroscopes are used to detect and measure the amplitude of the hand jitter and the image is shifted in software by a certain number of pixels. The system using gyroscopes has an advantage over optical image stabilization because there are no moving parts, and the power dissipation is much lower. Although continuously shrinking in size and price, the use of gyroscopic sensors is still an expensive option for camera or phones manufactures.
In the paper by Aaron Deever, entitled “In-camera all-digital video stabilization”, published in ICIS'06 conference, Rochester, May 2006, the problem of video stabilization was investigated with particular focus on in-camera, all-digital video stabilization or digital image stabilization (DIS). Algorithms for global camera motion estimation and jitter calculation were proposed by Deever. Computational constraints imposed by an in-camera solution are also discussed.
An image stabilizing apparatus for correcting motion of an image recording apparatus by using a bit-plane matching technique, and an image stabilizing method, are described in U.S. Pat. No. 6,535,244, entitled, “Image stabilizing apparatus using bit-plane Matching and Image Stabilizing Method Using the Same”. In the image stabilizing apparatus, a field memory stores input digital image information. A motion detecting circuit calculates an amount of movement of input image information between two screens by using bit-plane matching technique and outputs a motion vector of the image recording apparatus. A motion correcting circuit corrects the motion of the image recording apparatus by moving image information stored in the field memory in an opposite direction to the direction of the motion vector.
A method and apparatus for motion estimation is also described in United States published patent application no. US2006/171464. A method and apparatus are described for motion estimation in which the amount of computation can be reduced. The method for motion estimation includes storing an interblock match difference calculated for a previous matching block to be motion estimated. An interblock match difference is calculated for a current matching block to be motion estimated using the stored interblock match difference. Motion estimation is performed on the current matching block using the interblock match difference calculated for the current matching block.